The performance and reliability of rolling bearings are determined to a large degree by the materials from which the bearing components are made. Steels used for rolling bearings must be capable of being adequately hardened and must have high fatigue strength and wear resistance. Also, the structural and dimensional stability of the bearing components must be satisfactory at the operating temperatures that can be expected.
In so-called hub bearing units (HBU) for cars and truck hub units (THU), the hub forms a bearing race for the rolling elements. For such HBU/THU forgings, a steel grade named SAE 1055 is commonly used. The composition of this steel grade is the following: 0.50-0.60% C, 0.60-0.90% Mn, 0.050% S max and 0.040% P max. The rest is iron and ordinary impurities. The bearing race is commonly induction hardened.